If you’re still trying to wrap your around what SwiftUI’s GeometryReader/Proxy are capable of, you won’t find a better resource than this series of articles. Well written and even better researched. https://swiftui-lab.com/

While #SwiftUI is stealing the thunder of UI/AppKit, understanding how stacking views work on a deeper level is timeless knowledge. Every platform implementation is a slight rearrangement of the same concepts, incl. CSS flexbox and SwiftUI H/V/Z stacks.